1. Field of the Invention
The invention relates generally to the field of digital signal communications and channel allocation. More particularly, the invention relates to opening a communications stream between two communicating terminals that are already known and identified to one another.
2. Description of the Related Art
In data communications systems that share communications channels, a procedure must be implemented to allow different users to take turns using the channels. In many systems, users are allocated a channel for a limited period of time. Then the channel is de-allocated and allocated to another user. This is known as a circuit switched system. In circuit-switched systems extensive setup must be done so that subsequent packets do not need to carry the full routing information. The packets instead will always travel the same circuit until that circuit is switched. In other systems, channels are never allocated but are always shared. This kind of system requires no overhead signaling for channel allocation but must have some way of directing packets and of resolving conflicts. Such systems are typically called packet-switched because each packet contains the full routing information required to direct the packet to its intended destination. Packet switching requires no overhead in the setup but adds significant overhead to each packet.
More specifically, a circuit-switched system may have a set of control channels which, are dedicated for use in allocating and de-allocating traffic channels to the various users. If there are many users sending short data sets, the control channel can require a significant portion of the available communications bandwidth. If insufficient bandwidth is provided for the control channels then, at least for some traffic patterns, particularly ones with frequent requests for a short-lived channel, the control channels can be a bottleneck to system usage even when traffic channels are not fully utilized.
Control channel usage can be made more efficient by requiring a multistage handshake each time a circuit is opened. The control channel can be used for the first stage and other channels, such as traffic channels, can be used for the later stages. The process can be initiated on a paging or random access channel. This approach allows a special channel to be optimized for each function. However, each of the optimized channels will still consume communications bandwidth that then cannot be used for traffic.
Packet switched networks eliminate all of the control channel overhead. However, collisions must be accommodated in some way. Since channels are not assigned for the shared channel, unless all of the users are known and have consistent traffic patterns, the shared channel will be underutilized. In part, the underutilization will come from available transmission times that are not used and, in part, the underutilization will come from several users attempting to use the shared channel at the same time.
In systems in which terminals are not identified and properly synchronized before transmitting, a “training” period is needed. The training period occurs when a channel is opened to allow two wireless endpoints to synchronize or fine-tune their timing, frequency, power, and spatial processing. The training period increases latency because of the degraded performance until the training is complete. The training period may also degrade system capacity by increasing interference between channels.
The present invention can minimize the difficulty of opening communication channels. This allows channels to be used for very short durations without dedicating a large amount of the communications resources to overhead. As a result, the communications system can be packet-oriented rather than connection-oriented without being packet-switched. As a result, the communications system can efficiently create circuits which only deliver a few packets.
Among the difficulties to be minimized in opening communications are latency and contention between users. Latency between the time a channel is requested and the time it is granted can be reduced by optimizing the channel request and channel allocation messages and by pre-registering users on the network. Latency between the time a channel is granted and the time that full channel throughput is reached can be minimized by providing other channel characteristics and parameters along with the channel request. It can also be minimized using channel characteristics and parameters that have already been exchanged in an earlier registration session. Limits on system capacity due to contention between users can be reduced by limiting the number of messages required to request and grant a channel and by using in-band signaling for many exchanges.
The present invention can be regarded as a hybrid of packet-switched and circuit-switched systems. It can be regarded as being a circuit-switched system, which is heavily optimized to make it efficient for the circuits to last for only a few packets before being torn down. Alternatively, it can be regarded as being packet-switched, but having the facility to combine all higher-level packets that are available during a specified period of time into a single air interface “packet” (stream) so that the routing info is amortized over many of the higher-level packets.